1. Field of the Invention
The present invention relates to a vehicle steering mechanism, and in particular, to an improved tiltable and telescopically extensible steering shaft mechanism for a vehicle steering mechanism.
2. Description of the Prior Art
A vehicle steering mechanism including a conventional tiltable and telescopically extensible steering shaft mechanism disclosed in U.S. Pat. No. 4,785,684, issued on Nov. 26, 1988, and hereby incorporated by reference, is shown in FIG. 1. Steering mechanism 100 includes steering wheel 700 mounted on shaft 400 which is further supported by upper bracket 230. Lower screw shaft 600 and upper screw shaft 160 extend from stationary bracket 200. First nut member 210 is disposed around lower screw shaft 600 and second nut member 240 is disposed around upper screw shaft 160 for axial movement therealong when the screw shafts rotate. Support bracket 230 is disposed for pivotable motion about pivot pin 220 extending from first nut member 210 and pivot pin 250 extending from second nut member 240. Lower screw shaft 600 is rotated by a motor (not shown). Upper shaft 160 is also rotated by the motor through a clutch means (not shown). Rotation of lower shaft 600 or upper shaft 160 by the motor causes first nut member 210 or second nut member 240 to move along lower screw shaft 600 and upper screw shaft 160, respectively.
When the motor is operated to rotate lower screw shaft 600 to move first nut member 210 therealong, support bracket 230 pivots about pivot pins 220 and 250 causing tilting motion of steering wheel 700. When the motor rotates both upper shaft 160, through the clutch means, and lower shaft 600, both first nut member 210 and second nut member 240 move along lower shaft 600 and upper shaft 150 respectively, causing telescopic or axial translational movement of steering wheel 700 toward or away from the driver. However, since upper shaft 160 is positioned just above pivot pin 250, during tilting movement of steering wheel 700 due to movement of only first nut member 210 along lower screw shaft 600, an excessive level of force is applied to second nut member 240 tending to deform second nut member 240 and upper screw shaft 160. In order to compensate for this excessive force, both second nut member 240 and upper screw shaft 160 have been made of an extremely rigid and strong material to prevent deformation. However, even with the use of strong material, wear and tear of the elements occurs.